The present invention relates to a process for the production of low viscosity, sucrose-based polyether polyols.
Polyether polyols based on sucrose useful for the production of polyurethane rigid foams are known. These polyether polyols are typically produced by reacting sucrose with alkylene oxides in the presence of sodium hydroxide. (See, for example, J. W. Le Maistre, R. B. Seymour, J. Org. Chem. 782, 1948).
U.S. Pat. Nos. 3,085,085 and 3,153,002 describe the reaction of sucrose with ethylene oxide and propylene oxide at elevated temperatures using potassium hydroxide as a catalyst to produce sucrose hydroxyalkyl ethers.
Variations of the process described in these disclosures result in sugar ethers having functionalities which are significantly lower than the functionality of pure sucrose polyethers. This reduced functionality is due to the formation of glycols as a result of the reaction of water with epoxides.
U.S. Pat. No. 2,902,478 discloses a process in which sucrose is suspended in epoxide and reacts to form the polyether. This process has the advantage that no lowering of functionality by glycol formation takes place. The viscosity of such polyethers, however, is very high. In addition, such reactions may present safety problems in production plants.
U.S. Pat. No. 3,941,769 discloses a process in which sucrose is reacted with epoxide in an organic; dispersing agent such as benzene, toluene, ethylbenzene, xylene or chlorobenzene (boiling range 80.degree.-180.degree. C.). This process has some serious disadvantages. First, the dispersing agents lower the reaction capacity by 10-40%. Second, the dispersing agent must be removed at the end of the production process. The products obtained by this process are highly functional, highly viscous (104,000-400,000 mPa.multidot.s) due to the degree of alkoxylation, and have an intense brown color. The intense color results from undesirable side reactions and caramelization of the sucrose used.
U.S. Pat. No. 4,230,824 describes the production of high functionality polyethers (i.e., functionality &gt;6.5) based on sucrose and polyalkylene polyamines in which ethylene oxide or propylene oxide in toluene is used as the dispersing agent in a process which otherwise corresponds to that disclosed in U.S. Pat. No. 3,941,765. The product obtained has a Gardener color number of 12.
U.S. Pat. No. 4,996,310 discloses a process for the production of low viscosity, sucrose-based polyethers having a high ethylene oxide content, a functionality of 4.4-4.5, a viscosity of from 830 to 2500 mPa.multidot.s at 25.degree. C. and Gardener color numbers of from 10 to 40.
No process for the production of high functionality, low viscosity, light colored sucrose polyethers is known. The prior art processes discussed above only partly fulfill these requirements.